1. Field of the Invention
The invention relates to a protective sheath for a lifting accessory such as a roundsling, lifting strap or the like, the protective sheath being formed from a woven base fabric and having at least one rib which is carried by the woven base fabric, which rib projects outwards from the woven base fabric and is formed by a rib fibre which is interwoven with the woven base fabric.
The invention also relates to an accessory for lifting loads in which a protective sheath of this kind surrounds a core extending in the longitudinal direction of the lifting accessory which is formed from at least one fibre strand. Lifting accessories of this kind are typically roundslings, lifting straps or the like.
2. Description of Related Art
Lifting accessories of this kind are used to lift heavy loads. What is usually done in this case is that the given lifting accessory is passed around a projection from, or shoulder on, or opening in the object to be lifted and is then hooked into for example a hook on a crane. There is not, as a rule, any way of preventing at least parts of the lifting accessory from resting against the object to be lifted in this case. In the region where there is contact between the lifting accessory and the object to be lifted, there are high pressures per unit area and due to the relative movements which also occur at this point these result in increased wear. This is particularly critical when the lifting accessory is passed round a sharp edge or point.
In a situation like this, the protective sheath which surrounds the core of the lifting accessory is intended not only to prevent excessive abrasive wear but also to ensure that the core of the lifting accessory is not damaged by the high local loads.
Another function of protective sheaths of the kind being considered here is to protect the given lifting accessory against damage from cuts if it is not used properly, which damage may for example occur in the course of rough use on building sites if the lifting accessories are dragged over sharp-edged objects such as concrete reinforcing wires or the like or are run over by fork-lift trucks or other pieces of construction machinery.
To meet the requirements which exist in practical use, what have to date been used in practice are protective sheaths on the outside of which ribs extending in the longitudinal direction of the protective sheath are formed by weaving techniques and into which a reinforcement of textile wire is also woven. Lifting straps and roundslings which are provided with protective sheaths of this kind are known from EP 0 498 253 B1 and are offered for sale by the applicant on page 12 of its 2008 catalogues “Absturzsicherung” [Fall protection], “Heben” [Lifting], “Zurren” [Lashing] under the name “SupraPlus”. When there are high pressures per unit area, the ribs present on the outside of a protective sheath of this kind prevent there from being an excessively high chafing load on the woven base fabric of the protective sheath, thus giving the lifting accessory a working life which is, overall, extended. At the same time, a textile wire which is woven into the woven base fabric is able to reinforce it in such a way that the protective sheath is also able to withstand high loads acting in its longitudinal direction safely.
One possible way of producing roundslings which will carry even higher loads is described in WO 2007/071310 A1. The roundsling which is known from this publication has a core in which what are called high-performance fibres are included, and a protective sheath surrounding the core into which high-performance fibres are likewise worked. The ratio of the mass of the high-performance fibres in the core to the mass of the high-performance fibres in the protective sheath is to be 0.15 to 2.0 in this case. In the case of the roundsling known from WO 2007/071310 A1, what is intended to be obtained in this way is not only a particularly high lifting capacity but also high security against damage due to contact with sharp edges.
It is true that the roundsling known from WO 2007/071310 A1 does have improved lifting properties as a result of the high proportion of high-performance fibres which it has in its core and in its protective sheath which surrounds the core. However, the price which has to be paid for this is reduced flexibility and a commensurate worsening of its ease of handling. Practical studies are also showing that protective sheaths which, in the way disclosed in WO 2007/071310 A1, have a high proportion of high-performance fibres in their woven base fabric do not meet stringent requirement for protection against cuts caused by sharp-edged objects. Added to this is the fact that high proportions of high-performance fibres in the woven fabric of the protective sheath are found to be critical when the protective sheath is subjected to what is known as thermofixing.
Under the standards which apply to protective sheaths for lifting accessories, thermofixing of this kind is generally laid down for textile protective sheaths when there is a risk that, in the course of practical use, loops or other irregularities which might interfere with the protective function of the sheath may form in the textile fabric of the sheath. In the course of the thermofixing, adequate heating so consolidates the structure of the individual filaments in the woven fabric of the protective sheath that the filaments remain in their positions in the woven fabric even when the protective sheath is deformed in practical use. The woven fabric shrinks at the same time and the non-interwoven core surrounded by the protective sheath is thus more satisfactorily gripped. Finally, the thermofixing may also be deliberately employed to partially melt the synthetic fibres of a woven fabric and to bond them together. It has been found that, in the course of thermofixing of this kind, there is an appreciable reduction in the strength properties of high-performance fibres of the kind being considered. Also, a high proportion of high-performance fibres impedes the desired consolidation of the woven fabric of the protective sheath.